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Pulmonary clearance of welding fume particles as assessed by magnetometry and confocal microscopy.

Pulmonary responses to welding exposures may vary due to the materials used during welding. Welding fume was collected during shielded electric arc welding from two types of consumable electrode wire: stainless steel (SS) and mild steel (MS). The objectives were to analyze the composition of the samples, describe the pulmonary clearance kinetics of the two fumes, and develop methods for imaging fume particles in the lungs. Bulk analysis of the metal constituents of the fume was characterized by energy dispersive spectroscopy (SS: 52.3% Fe, 22.2% Cr, 18.3% Mn, 4.9% Ni, 2.3% Si; MS: 89.2% Fe, 8.2% Mn, 2.6% Si). CD/VAF rats (n=4) were intratracheally instilled (1 mg/100 g b wt) with the SS or MS welding fume samples suspended in sterile saline. At 1, 7, and 14 days post-instillation, the lungs were removed. Due to the magnetic nature of the welding fumes, the quantity of particles present in the lungs could be assessed by magnetometry. The MS welding fume was eliminated from the lungs faster (p<0.05) than the SS welding fume. By 14 days, 35.5% of the initial dose of the MS particles but only 7.7% of the SS particles had been cleared from the lung. Images of particles in lung tissue were generated by confocal microscopy of aldehyde-fixed, fluorescent-stained (Lucifer Yellow CH; 0.1 mg/ml) lung pieces embedded in Spurr's epoxy. Images were recorded from a laser scanning confocal microscope fitted with an argon-ion laser using the 488 nm excitation light. With a fluorescent emission spectra >510 nm, lung tissue and cells were imaged. When using polarized light <510 nm simultaneously passed to a separate optical path, images of welding fume in the lungs were recorded which were suitable for quantitation. We have developed a method to image particles in lungs and have shown that welding fumes of different composition are cleared at different rates.